The Cl 1604 supercluster at z ∼ 0.9 is one of the most extensively studied high-redshift large-scale structures, with more than 500 spectroscopically confirmed members. It consists of eight clusters ...and groups, with members numbering from a dozen to nearly a hundred, providing a broad range of environments for investigating the large-scale environmental effects on galaxy evolution. Here we examine the properties of 48 post-starburst galaxies in Cl 1604, comparing them to other galaxy populations in the same supercluster. Incorporating photometry from ground-based optical and near-infrared imaging, along with Spitzer mid-infrared observations, we derive stellar masses for all Cl 1604 members. The colors and stellar masses of the K+A galaxies support the idea that they are progenitors of red sequence galaxies. Their morphologies, residual star formation rates, and spatial distributions suggest that galaxy mergers may be the principal mechanism producing post-starburst galaxies. Interaction between galaxies and the dense intracluster medium (ICM) is also effective, but only in the cores of dynamically evolved clusters. The prevalence of post-starburst galaxies in clusters correlates with the dynamical state of the host cluster, as both galaxy mergers and the dense ICM produce post-starburst galaxies. We also investigate the incompleteness and contamination of K+A samples selected by means of Hδ and O II equivalent widths. K+A samples may be up to ∼50% incomplete due to the presence of LINERs/Seyferts, and up to ∼30% of K+A galaxies could have substantial star formation activity.
We present the first results of a search for Ly alpha emitters (LAEs) in the DEEP2 spectroscopic database that uses a search technique that is different from but complementary to traditional ...narrowband imaging surveys. We have visually inspected image20% of the available DEEP2 spectroscopic data and have found nine high-quality LAEs with clearly asymmetric line profiles and an additional 10 objects of lower quality, some of which may also be LAEs. Our survey is most sensitive to LAEs at image and that is indeed where all but one of our high-quality objects are found. We find the number density of our spectroscopically discovered LAEs to be consistent with those found in narrowband imaging searches. The combined, averaged spectrum of our nine high-quality objects is well fit by a two-component model, with a second, lower amplitude component redshifted by image420 km s super(-1) with respect to the primary Ly alpha line, consistent with large-scale outflows from these objects. We conclude by discussing the advantages and future prospects of blank-sky spectroscopic surveys for high-z LAEs.
We report the discovery of a spectroscopically confirmed strong Lyαemitter atz=7.0281±0.0003, observed as part of the Reionization Lensing Cluster Survey(RELICS). This galaxy, dubbed“Dichromatic ...Primeval Galaxy”atz∼7(DP7), shows two distinct components. While fairly unremarkable in terms of its ultraviolet(UV)luminosity(~L0.3UV*,whereLUV*is the characteristic luminosity), DP7 has one of the highest observed Lyαequivalent widths(EWs)amongLyαemitters atz>6(>200Åin the rest frame). The strong Lyαemission generally suggests a young metal-poor, low-dust galaxy; however, we find that the UV slopeβof the galaxy as a whole is redder than typical star-forming galaxies at these redshifts,−1.13±0.84, likely indicating, on average, a considerable amount of dust obscuration, or an older stellar population. When we measureβfor the two components separately, however, we find evidence of differing UVcolors, suggesting two separate stellar populations. Also, we find that Lyαis spatially extended and likely larger than the galaxy size, hinting to the possible existence of a Lyαhalo. Rejuvenation or merging events could explain these results.Either scenario requires an extreme stellar population, possibly including a component of Population III stars, or an obscured active galactic nucleus. DP7, with its low UV luminosity and high LyαEW, represents the typical galaxies that are thought to be the major contribution to the reionization of the universe, and for this reason DP7 is an excellent target for follow-up with the James Webb Space Telescope
The stellar mass-halo mass relation is a key constraint in all semi-analytic, numerical, and semi-empirical models of galaxy formation and evolution. However, its exact shape and redshift dependence ...remain under debate. Several recent works support a relation in the local universe steeper than previously thought. Based on comparisons with a variety of data on massive central galaxies, we show that this steepening holds up to z ~ 1 for stellar masses M sub(star) > ~ 2 x 10 super(11) M sub(middot in circle). Specifically, we find significant evidence for a high-mass end slope of beta > ~ 0.35-0.70 instead of the usual beta <, ~ 0.20-0.30 reported by a number of previous results. When including the independent constraints from the recent Baryon Oscillation Spectroscopic Survey clustering measurements, the data, independent of any systematic errors in stellar masses, tend to favor a model with a very small scatter (<, ~0.15 dex) in stellar mass at fixed halo mass, in the redshift range z < 0.8 and for M sub(star) > 3 x 10 super(11) M sub(middot in circle), suggesting a close connection between massive galaxies and host halos even at relatively recent epochs. We discuss the implications of our results with respect to the evolution of the most massive galaxies since z ~ 1.
We study the stellar population properties of the IRAC-detected 6 less than or similar to z less than or similar to 10 galaxy candidates from the Spitzer UltRa Faint SUrvey Program. Using the Lyman ...Break selection technique, we find a total of 17 galaxy candidates at 6 less than or similar to z less than or similar to 10 from Hubble Space Telescope images (including the full-depth images from the Hubble Frontier Fields program for MACS 1149 and MACS 0717) that have detections at signal-to-noise ratios \textgreater= 3 in at least one of the IRAC 3.6 and 4.5 mu m channels. According to the best mass models available for the surveyed galaxy clusters, these IRAC-detected galaxy candidates are magnified by factors of similar to 1.2-5.5. Due to the magnification of the foreground galaxy clusters, the rest-frame UV absolute magnitudes M-1600 are between -21.2 and -18.9 mag, while their intrinsic stellar masses are between 2 x 10(8)M(circle dot) and 2.9 x 10(9)M(circle dot). We identify two Ly alpha emitters in our sample from the Keck DEIMOS spectra, one at z(Ly alpha) = 6.76 (in RXJ 1347) and one at z(Ly alpha) = 6.32 (in MACS 0454). We find that 4 out of 17 z greater than or similar to 6 galaxy candidates are favored by z less than or similar to 1 solutions when IRAC fluxes are included in photometric redshift fitting. We also show that IRAC 3.6-4.5 color, when combined with photometric redshift, can be used to identify galaxies which likely have strong nebular emission lines or obscured active galactic nucleus contributions within certain redshift windows.
Abstract
The second most significant detection of the Planck Sunyaev−Zel’dovich survey, PLCK G287.0+32.9 (
z
= 0.385), boasts two similarly bright radio relics and a radio halo. One radio relic is ...located
NW of the X-ray peak and the other
Mpc to the SE. This large difference suggests that a complex merging scenario is required. A key missing puzzle for the merging scenario reconstruction is the underlying dark matter distribution in high resolution. We present a joint Subaru Telescope and
Hubble Space Telescope
weak-lensing analysis of the cluster. Our analysis shows that the mass distribution features four significant substructures. Of the substructures, a primary cluster of mass
dominates the weak-lensing signal. This cluster is likely to be undergoing a merger with one (or more) subcluster whose mass is approximately a factor of 10 lower. One candidate is the subcluster of mass
located
to the SE. The location of this subcluster suggests that its interaction with the primary cluster could be the source of the NW radio relic. Another subcluster is detected
Mpc to the SE of the X-ray peak with mass
. This SE subcluster is in the vicinity of the SE radio relic and may have created the SE radio relic during a past merger with the primary cluster. The fourth subcluster,
, is NW of the X-ray peak and beyond the NW radio relic.
Recent observations have revealed the presence of strong CIII emission (EW CIII > 20Å) in z > 6 galaxies, the origin of which remains unclear. In an effort to understand the nature of these line ...emitters, we have initiated a survey targeting CIII emission in gravitationally-lensed reionization era analogs identified in HST imaging of clusters from the RELICS survey. Here we report initial results on four galaxies selected to have low stellar masses (2-8×10 7 M) and J 125-band flux excesses indicative of intense OIII+Hβ emission (EW OIII+Hβ =500-2000Å), similar to what has been observed at z > 6. We detect CIII emission in three of the four sources, with the CIII EW reaching values seen in the reionization era (EW CIII 17 − 22Å) in the two sources with the strongest optical line emission (EW OIII+Hβ 2000Å). We have obtained a Magellan/FIRE near-infrared spectrum of the strongest CIII emitter in our sample, revealing gas that is both metal poor and highly ionized. Using photoionization models, we are able to simultaneously reproduce the intense CIII and optical line emission for extremely young (2-3 Myr) and metal poor (0.06-0.08 Z) stellar populations, as would be expected after a substantial upturn in the SFR of a low mass galaxy. The sources in this survey are among the first for which CIII has been used as the primary means of redshift confirmation. We suggest that it should be possible to extend this approach to z > 6 with current facilities, using CIII to measure redshifts of objects with IRAC excesses indicating EW OIII+Hβ 2000Å, providing a method of spectroscopic confirmation independent of Lyα.
We present the most distant detection of cosmic voids (z ∼ 2.3) and the first detection of three-dimensional voids in the Ly forest. We used a 3D tomographic map of the absorption with an effective ...comoving spatial resolution of 2.5 h−1 Mpc and a volume of 3.15 × 105 h−3 Mpc3, which was reconstructed from moderate-resolution Keck I/LRIS spectra of 240 background Lyman-break galaxies and quasars in a 0.16 deg2 footprint in the COSMOS field. Voids were detected using a spherical overdensity finder calibrated from hydrodynamical simulations of the intergalactic medium (IGM). This allows us to identify voids in the IGM corresponding to voids in the underlying matter density field, yielding a consistent volume fraction of voids in both data (19.5%) and simulations (18.2%). We fit excursion set models to the void radius function and compare the radially averaged stacked profiles of large voids (r > 5 h−1 Mpc) to stacked voids in mock observations and the simulated density field. Comparing with 432 coeval galaxies with spectroscopic redshifts in the same volume as the tomographic map, we find that the tomography-identified voids are underdense in galaxies by 5.95 compared to random cells.
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